Insert node of linked list at the end but program keep crashing

Question

As the title say, I tried to insert node of linked list at the end but C++ program keep crashing

class SymbolTable
{
 struct Node
 {
 string id;
 int num;
 string str;
 Node *next;
 };
public:
 SymbolTable() {}
 void insert(string id);
private:
 Node head = { "head", -99, "", nullptr};
};
void SymbolTable::insert(string id)
{
 Node *traverser = &(this->head);
 while (traverser != nullptr) { traverser = traverser->next; }
 Node *newNode = new Node();
 newNode->id = id;
 newNode->next = nullptr;
 traverser->next = newNode; // --> Crashing
}

I don't see any problem.

Answer:

traverser != nullptr should be traverser->next != nullptr

• Yksisarvinen: Think for a while what traverser is when the loop ends. What condition must be met for the loop to end?
• Tan Nguyen: Ugrh... I was doing right ._. Why I change that line ._.
• Chris: Aesthetic note: your while loop could easily be a for loop. E.g. for (traverser = &(this->head); traverser != nullptr; traverser = traverser->next);
• Tan Nguyen: @Chris Wow! OwO
• Thomas Matthews: Why do you have a head node instead of a pointer to the first node? There is no need for a head node.

Answer 1

I do find few problems, first of all in-class definition you declared function insert as:

void insert(string id, string type);

however, when you declare a function outside of it you skipped 2nd argument:

void SymbolTable::insert(string id);

I don't understand how this code would even compile. I also fixed algorithm itself:

void SymbolTable::insert(string id)
{
 Node* traverser = &(this->head);
 while (traverser->next != nullptr) //used to be (traverse !=nullptr)
 { 
 traverser = traverser->next;
 }
 Node* newNode = new Node();
 newNode->id = id;
 newNode->next = nullptr;
 traverser->next = newNode; 
}

Issue was that you were checking if traverse is null, not if the next of traverser is null. In consequence, you were referring to traverser which was a nullpointer. After this little fix code compiles just fine after inserting.

• Tan Nguyen: I forget to remove when edit code to post. But thanks anyway